LogDog: Add Butler stream server package.

client/logdog/butlerlib/streamclient/registry.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package streamclient
+
+import (
+        "fmt"
+        "strings"
+        "sync"
+)
+
+var (
+        // defaultRegistry is the default protocol registry.
+        defaultRegistry = &protocolRegistry{}
+)
+
+// protocolRegistry maps protocol prefix strings to their Client generator
+// functions.
+//
+// This allows multiple Butler stream protocols (e.g., "unix:", "net.pipe:",
+// etc.) to be parsed from string.
+type protocolRegistry struct {
+        sync.Mutex
+
+        // protocols is the set of registered protocols. Each client should register
+        // via registerProtocol in its init() method.
+        protocols map[string]clientFactory
+}
+
+func (r *protocolRegistry) register(name string, f clientFactory) {
+        r.Lock()
+        defer r.Unlock()
+
+        if _, ok := r.protocols[name]; ok {
+                panic(fmt.Errorf("streamclient: protocol already registered for [%s]", name))
+        }
+        if r.protocols == nil {
+                r.protocols = make(map[string]clientFactory)
+        }
+        r.protocols[name] = f
+}
+
+// newClient invokes the protocol clientFactory generator for the
+// supplied protocol/address string, returning the generated Client.
+func (r *protocolRegistry) newClient(path string) (Client, error) {
+        parts := strings.SplitN(path, ":", 2)
+        params := ""
+        if len(parts) == 2 {
+                params = parts[1]
+        }
+
+        r.Lock()
+        defer r.Unlock()
+
+        if f, ok := r.protocols[parts[0]]; ok {
+                return f(params)
+        }
+        return nil, fmt.Errorf("streamclient: no protocol registered for [%s]", parts[0])
+}
+
+// registerProtocol registers a protocol with the default (global) protocol
+// registry.
+func registerProtocol(name string, f clientFactory) {
+        defaultRegistry.register(name, f)
+}